Fibre lasers are increasingly being used for material processing applications such as welding, cutting and marking. Their advantages include high efficiency, robustness and high beam quality. Examples include femtosecond lasers for multiphoton processing such as the imaging of biological tissues, Q-switched lasers for machining applications, and high-power continuous-wave lasers.
Traditional lasers used for material processing applications predominate at around 1.06 μm and longer wavelengths such as provided by a carbon dioxide laser (10.6 μm). These lasers are being supplemented by fibre lasers operating at around 1.06 μm. Light scattered from the work piece when using such fibre lasers is a problem because the scatter is at wavelengths at which the retina of the eye can be easily damaged.
It is desirable to have eye safe wavelengths for scatter light considerations. This means wavelengths longer than 1400 nm, and preferably between 1500 nm and 2500 nm. Erbium is a suitable dopant for fibre lasers outputting in the 1550 nm wavelength window. Erbium doped fibres can be pumped at a variety of wavelengths, including by high-power diode lasers operating between 915 nm and 980 nm. Unfortunately, the erbium doped fibre is not very efficient when pumped at 915 nm and this leads to undesirable heat generation within the erbium doped fibre.
It is also desirable to improve the thermal management of fibre lasers so as to reduce the problem of heat generation within a high power fibre laser. The main source of heat generation is due to the quantum defect (ie the difference in photon energy between the pump and the laser photons).
It is also preferable to use an optical fibre material that has good heat resistance, low loss properties, and that can be fusion spliced.
Laser diodes have reduced life if they are pulsed and this therefore limits the life of high power fibre lasers that are pumped by pulsed laser diodes. A solution is to accept diode failures and to provide redundancy. Commercial systems available today can use between 10% and 20% more laser diodes than would otherwise be required if the laser diodes were more reliable. It would be an advantage to improve the reliability of pulsed fibre lasers that are pumped by laser diodes.
An aim of the present invention is to provide an apparatus for providing optical radiation that reduces at least one of the above aforementioned problems.